Buff

A buff is a change to a gameplay mechanic that is either perceived as positive or wanted.
For example: If a spell or skill gets updated to damage or heal for more, cost less to cast, or has a shorter recharge, it has been buffed.
In this way a buff is the opposite of a nerf.

Because enchantments are the most common type of buffs in Guild Wars, buff is also used within the context of the game as a synonym for enchantment. For example when a player is asking his or her party members for a buff.